A Phase 1b Study of Step-up Dosing with ABBV-383, a B-Cell Maturation Antigen (BCMA) x CD3 Bispecific Antibody, in Patients with Relapsed or Refractory Multiple Myeloma

Abstract

Introduction Patients (pts) with multiple myeloma (MM) eventually become refractory to current treatments. There is an unmet need for new therapies with durable effcacy, favorable safety, and simpliied dosing schedules. ABBV-383 is a unique BCMA x CD3 bis-peciic antibody T-cell engager comprising bivalent high-avidity BCMA binding domains, a low-affnity CD3-binding domain designed to minimize cytokine release and the risk for cytokine release syndrome (CRS), and a silenced Fc tail for extended half-life enabling dosing convenience. In an ongoing grst-inhuman (FIH) study (NCT03933735) in heavily pretreated pts with relapsed or refractory (RR) MM, ABBV-383 monotherapy (60 mg Q4W) resulted in deep and durable responses. Introduction of a modiied dexamethasone (Dex) premedication (premed) schedule in cycle (C) 1 lowered incidence and severity of CRS (43% overall; 5% grade ≥2) vs pts treated with low Dex (71% overall; 20% grade ≥2) (JCO 2024;42[suppl 16]:7531). We now report results of Arm A of the open-label, phase 1b study (NCT05650632) evaluating 1 step-up dose (SUD) of ABBV-383 as a strategy to mitigate the risk of severe CRS and further assess ABBV-383 activity in pts with RRMM. Methods This study is enrolling pts with RRMM, ECOG performance status ≤2, and documented evidence of progression during or after the last treatment. Pts must have received ≥3 prior lines of therapy, including a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 monoclonal antibody. Arm A consists of a dose-optimization (DO) and a dose-expansion (DE) part. During DO, pts received a single SUD of intravenous ABBV-383 (2/4 mg) on C1 day (D) 1, followed by the target dose of 60 mg on D4. In the DE, based on DO Ondings, pts received the recommended ABBV-383 SUD on C1D1, followed by 60 mg on D4. The modiied premed schedule that lowered incidence and severity of CRS in the FIH study was also introduced prior to target dose on C1D4. After C1, pts received 60 mg ABBV-383 Q4W on D1 of each cycle for DO and DE until disease progression,